21 



EMBRYONIC DEVELOPMENT. 



Owing to the transparency of the egg membranes, something- of 

 the development of the embryo can be seen through them, but no 

 special study has yet been made upon the subject of the embryology 

 of the weevil. The fully developed embryo completely fills the inte- 

 rior of the egg, its large head being in one end and its body curved 

 ventrally upon itself till nearly double. Considerable motion is mani- 

 fested if the egg be touched at this period. 



LENGTH OF EGG STAGE. 



Concealed as the eggs are beneath several layers of vegetable tis- 

 sue, it is impossible to examine them to ascertain the exact length of 

 the egg stage without in some degree interfering with the naturalness 

 of the accompanying conditions. The beginning of the stage was 

 easily obtained by confining female weevils with uninfested squares. 

 Careful dissections were then made of the squares at a little later 

 than what was found to be the average embryonic period at that sea- 

 son. In this way it is believed the range of error was reduced to a 

 fraction of a day in most cases, and a large number of observations 

 were made to still further reduce the error. 



As shown by Table I, 553 observations have been recorded upon 

 this point, the majority of the observations being made in the fall of 

 1902. Considering the temperatures prevailing at the four periods 

 studied, it appears that the range in development during the average 

 season at Victoria, Tex., has been included, and it seems probable 

 that from these temperatures as a basis the length of the egg stage 

 can be approximately determined for any season and for any locality 

 within the present area of infestation. 



Table I. — Leiu/th of egg stage at certain periods. 



Period of examination. 



Number 

 of obser- 

 vations. 



Mean 

 tempera- 

 ture for 

 period. 



Average 

 effective 

 tempera- 

 ture." 



Average 



length of 



egg 



stage. 



1902. 

 September 4-October 3 . . . 



385 



lo- 

 ss 



25 



°F. 

 81 

 73 

 62 



72.5 



°F. 

 38 

 30 

 19 



32.5 



Days. 

 2. 5 to 3 



October 7-November 13 . 



4 to 4.5 



November 27-December 15 



11 



1903. 



3. 5 to 4 







Total 



553 







bSAto 4.1 











«In considering the influence of temperature upon the weevils it has been assumed that, as has 

 been found to be the case with other animals, 43° P. would be about the lowest temperature at 

 which the weevils would be active. Temperatures b3low that point would have, therefore, no 

 influence upon their activity, while all above that point would. For this reason it is better to 

 speak of the " effective temperature.' 1 meaning by that the number of degrees above 43° F. 

 Experiments made upon the influence of temperature upon the activity of weevils indicate 

 that this is very near the correct figure for this insect. 



b Weighted average. 



The extreme range observed in Table II in the length of this stage 

 is from two to fifteen days, while the average period for the whole 



